This invention relates to a process for increasing the production of benzene, toluene, and xylenes (BTX) and ethylbenzene from a C.sub.9.sup.+ aromatics-containing naphtha by a modified pretreatment of raw naphtha. The process also permits a reformer to process heavier naphthas, including FCC heavy gasoline and coker naphtha.
C.sub.9.sup.+ aromatics are found in heavy naphthas, e.g., FCC heavy gasoline, and coker heavy naphtha. Restrictions on the content of these heavy aromatics in gasolines will result from proposed end boiling point limits of gasoline fuels, referred to as T90 or (90 vol % temperature). T90 limits curtail the presence of hydrocarbon components that boil above temperatures in a range of 350.degree. to 430.degree. F. C.sub.6 to C.sub.8 aromatics include BTX (benzene, toluene, and xylenes), as well as EB (ethylbenzene). Inasmuch as the C.sub.6 to C.sub.8 aromatics have a higher value commercially than C.sub.9.sup.+ aromatics, the conversion of C.sub.9.sup.+ aromatics in heavy naphthas to C.sub.6 to C.sub.8 aromatics is highly desirable.
C.sub.6 to C.sub.8 aromatics contribute to the octane rating of the gasoline pool in a refinery, and are commonly produced in refinery processes such as catalytic reforming which have been a part of the conventional refinery complex for many years. However, recent concerns about volatility and toxicity of hydrocarbon fuel and the resultant environment damage has prompted legislation that limits the content and composition of aromatic hydrocarbons in such fuels. Some of these limitations relate specifically to benzene which, due to its toxicity, will be substantially eliminated from the gasoline pool.
However, because C.sub.6 to C.sub.8 aromatics are commercially desirable petrochemicals, it would be desirable to provide a process for reforming lower value heavy naphtha feedstocks which produces low aromatics content gasoline, as well as C.sub.6 to C.sub.8 aromatics which can be thereafter extracted from the reformate product.
Reformates can be prepared by conventional techniques by contacting any suitable material such as a naphtha charge material boiling in the range of C.sub.5 or C.sub.6 up to about 380.degree. F. (193.degree. C.) with hydrogen in contact with any conventional reforming catalyst.
U.S. Pat. No. 4,927,521 to Chu, incorporated herein by reference, discloses a process for pretreating naphtha prior to reforming, by contacting with a zeolite catalyst, e.g., zeolite beta, containing at least one noble metal and at least one alkali metal, for the purpose of producing higher yields of C.sub.4.sup.+ and C.sub.5.sup.+ gasolines.
U.S. Pat. No. 5,320,742 to Fletcher, et al., incorporated herein by reference, discloses a process for upgrading a higher boiling sulfur-containing catalytically cracked naphtha by hydrodesulfurization followed by contact with an intermediate pore zeolite, e.g., zeolite beta, under conditions which crack low octane paraffins to form higher octane lighter paraffins and olefins.